Over the last five years, this laboratory has compiled extensive evidence suggesting that the retinoblastoma gene product (pRb) plays a central role in prostate homeostasis through its ability to regulate epithelial growth and survival. However, the lethal nature of the Rb knockout in the mouse embryo has precluded gene disruption experiments to examine this role for Rb. To circumvent this problem and to address Rb functional studies, my laboratory has utilized an innovative approach to "rescue" Rb-/- prostate precursor rudiments from mouse embryos prior to their death resulting in the generation of viable Rb-/- prostate tissue and Rb-/- prostate epithelial cell lines. This model provides a unique experimental platform with which to investigate the consequences of Rb deletion on prostate epithelial physiology. Using this technique, we have made the compelling observation that the loss of Rb results in a non-transformed phenotype that exhibits increased expression of androgen receptor (AR) protein and mRNA and increased AR transcriptional activity. These findings strongly suggest that Rb and AR are interacting components of a precisely regulated, but poorly understood mechanism that control the growth and survival of prostate epithelium. We hypothesize that the loss of Rb results in the activation of a transcriptional co-factor, E2F1, which induces AR transcription in prostate epithelial cells. The proposed studies will determine the role of Rb/E2F1 in the regulation of AR transcription and AR activity in cultured prostate epithelial cells and in recombinant prostate tissue in vivo. We will also determine if Rb deletion results in increased AR responsiveness to paracrine growth factors secreted by prostate stromal cells and elucidate the specific signaling pathways that regulate AR function in this hormone-independent mechanism.